A rotational speed detection mechanism has been attached to, for example, an automotive wheel bearing apparatus for detecting a rotational speed of a wheel in order to control an Antilock Brake System (ABS), a Traction Control System (TCS), or the like. The rotational speed detection mechanism is made up of a magnetic ring or the like and a rotational speed sensor. The magnetic ring or the like is provided on a rotational member that rotates integrally with the wheel, such that the magnetic characteristics thereof cyclically change circumferentially. The rotational speed sensor is provided on a member fixed to an automotive body. In this case, the magnetic ring or the like is attached to an inner member (inner race) side of the wheel bearing apparatus, and the rotational speed sensor is attached to an outer member (outer race) side.
Patent Documents 1 to 5 disclose technical concepts in which the magnetic ring is assembled integrally with a hub bearing, in view of attachment (assembly) workability, replacement workability, the installation space, and so on.
Also, seal members have been provided for preventing entry of water or the like into the hub bearing. Patent Documents 1 to 5 consider sealing performance for a hub bearing, as well as the positional relationship between a magnetic ring and a rotational speed sensor.
Further, Patent Documents 6 to 9 disclose technical concepts related to improving the sealing performance for a hub bearing using various seal members.
In the above-mentioned conventional sealing structures, however, a seal member is disposed in the vicinity of the balls of a hub bearing. For example, water, muddy water or the like, which enters around the seal member, adversely affects the rotational speed sensor that is arranged in the vicinity of the hub bearing.
Also, when the above-mentioned conventional sealing structures are applied to a bearing apparatus for a wheel, in an independent four-wheel drive vehicle for example, and a large amount of muddy water or the like is splashed by the front wheels of the independent four-wheel drive vehicle, it is hard to prevent such muddy water from entering inside passages which are in communication with the hub bearings in the rear wheels. Thus, the rotational speed sensors arranged in such passages in communication with the hub bearings cannot be suitably protected.
Further, the above-mentioned conventional sealing structures center on the prevention of entry of water, muddy water or the like, but do not consider ways of discharging water, muddy water or the like that has already entered.
Patent Document 1: Japanese Laid-Open Patent Publication No. 3-279061;
Patent Document 2: Japanese Laid-Open Patent Publication No. 6-308145;
Patent Document 3: Japanese Laid-Open Patent Publication No. 2001-83166;
Patent Document 4: Japanese Laid-Open Patent Publication No. 2000-221203;
Patent Document 5: Japanese Laid-Open Patent Publication No. 2004-132782;
Patent Document 6: Japanese Laid-Open Patent Publication No. 2001-294011;
Patent Document 7: Japanese Laid-Open Patent Publication No. 2002-172912;
Patent Document 8: Japanese Laid-Open Patent Publication No. 2003-175701; and
Patent Document 9: Japanese Laid-Open Utility Model Publication No. 63-133641.